1. Field of the Invention
This invention relates to a power semiconductor device having a large pellet size and used for motor control or the like.
2. Description of the Related Art
In a power semiconductor module, the technique utilizing the direct bonding of copper to ceramic is disclosed in, for example, U.S. Pat. No. 3,994,430 and IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. ED-23, NO. 8, AUGUST 1976, p 964, "A New Hybrid Power Technique Utilizing a Direct Copper to Ceramic Bond".
In the power semiconductor module utilizing the above technique, a built-in device is fixed on a plate called a direct bond copper (DBC) plate and constituted by directly attaching copper (Cu) to a ceramic plate. A heat sink is fixed on the rear surface of the DBC plate which is the opposite surface of the fixing surface of the device. With this construction, the number of manufacturing steps and the number of parts used can be reduced.
FIG. 1 is a perspective view of a conventional DBC plate fixed on a heat sink. A heat sink 1 may be formed of a Cu plate plated with nickel or aluminum plate, for example. A DBC plate 2 is fixed on the heat sink 1. The DBC plate 2 has a Cu plate 4 which is fixed on the surface of a ceramic plate 3 and on which a semiconductor pellet (not shown) is mounted and Cu plates 5 used as electrodes of the semiconductor pellet and fixed on the surface of the ceramic plate. The ceramic plate 3 and the Cu plates 4 and 5 are fixed together in a high-temperature oxidation atmosphere, for example. Although not shown in FIG. 1, a Cu plate is also fixed on the rear surface of the ceramic plate 3.
The DBC plate 2 is fixed on the heat sink 1 by soldering, for example. The ceramic plate 4 which is insulative is disposed between the Cu plate 4 and the heat sink 1. In a case where a product requiring that the Cu plate 4 on which the semiconductor pellet is disposed and the heat sink 1 are electrically connected is manufactured, a terminal metal member 6 is formed. The terminal metal member 6 is bonded at one end to the Cu plate 4 and bonded at the other end to the heat sink 1. With this connection, the Cu plate 4 on which the semiconductor pellet is disposed is electrically connected to the heat sink 1.
However, mounting of the terminal metal member 6 makes it difficult to attain automation of the mass-production line. First, it is difficult to use the mass-production line together with a mass-production line in which mounting of the terminal metal member 6 is not necessary. Secondly, enhancement of the mass-productivity is prevented by the adhesive quality and the precision of the mounting position of the terminal metal member 6.